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Thank youYou can call US border security, just google their number and ask them. However, if the person has a valid work/study permit without a TRV, they can still re-enter Canada.
In order to return to Canada to study/work, it is important to carry a:
Valid passport or travel document*, and
Valid study permit/work permit.
If you are from a country whose citizens need a Temporary resident visa (TRV) to travel to Canada, you will also need a valid TRV to return, unless you:
Are returning to Canada after visiting only the United States** or St. Pierre and Miquelon, and
Will return before your study permit expires or any extension to it.